1. Field of the Invention
The present invention relates to a semiconductor optical device including a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor and a method of manufacturing the same.
2. Description of the Related Art
It is known to utilize a semiconductor layer formed on a semiconductor substrate for an optical waveguide. A device wherein a semiconductor optical amplifier using an InGaAsP active layer and an optical waveguide using InGaAsP for a core are integrated on an InP substrate, which is used in a network using light having the wavelength of 1.25 to 1.65 xcexcm suitable for transmission on an optical fiber is also known.
The emission wavelength of a semiconductor laser and a semiconductor optical amplifier respectively adopting an InP semiconductor can be varied so that it covers a range of 1.25 to 1.65 xcexcm. An optical device wherein optical elements such as a semiconductor optical amplifier and a diffraction grating are integrated on a single InP semiconductor substrate can be produced.
As a result of the review of such an optical device, the inventors discovered the following problems.
To integrate optical elements such as a semiconductor optical amplifier and a diffraction grating on a single semiconductor substrate, large area is required. However, it is technically difficult to manufacture a fine InP semiconductor wafer having a large aperture and suitable for an integrated circuit. Also, to manufacture an InP semiconductor substrate, high-priced material is required to be used.
In the meantime, when the application of optical communication is considered to be enlarged in future, a low-priced wafer and a wafer suitable for large scale integration are required more and more. Therefore, it becomes important to select low-priced semiconductor material of which a wafer suitable for large scale integration can be manufactured.
These inventors think that for such a semiconductor substrate, a GaAs semiconductor substrate is the most suitable.
However, when a GaAs semiconductor substrate is adopted, it next becomes important to select semiconductor material suitable for integrating optical elements such as a luminous element, an optical waveguide and a diffraction grating on the substrate. Then, these inventors researched on such semiconductor material. As a result, the following some documents found.
For a document related to a semiconductor laser, Japanese Patent Unexamined Publication No. Hei. 7-154023 can be given. In the document 1, an invention made to solve a problem that it is difficult to form a semiconductor laser having high characteristic temperature for irradiating a laser beam having the wavelength of 1.3 xcexcm on an InP substrate is disclosed. To solve the problem, in the document 1, a semiconductor laser provided with a GaAs semiconductor substrate and a GaInNAs semiconductor active layer the composition of nitrogen (N) of which is 0.5% or more on the substrate is disclosed. The oscillation wavelength of 1.3 xcexcm of the semiconductor laser is acquired in a state in which the compressive strain quantity of a distorted GaInAsN layer does not exceed 2% because nitrogen is mixedly crystallized. However, in this invention, there is no description of a problem when plural different optical elements are integrated on a single substrate.
Also, for such a document, Japanese Patent Unexamined Publication No. Hei. 6-37355 can be given. In this document 2, an invention made to provide new semiconductor material that can oscillate a laser beam of a short wavelength is disclosed. It is described that it is possible to provide a semiconductor laser that can continuously oscillate a laser beam of a wavelength in a range of 0.35 to 1.2 xcexcm in case where a GaAsN semiconductor is adopted for material to achieve the object is enabled. Also, in this document, a GaInNAs semiconductor is described. According to this description, the GaInNAs semiconductor can relieve the mismatching in a lattice constant with the GaAs semiconductor. There is also only description that a luminous element of a longer wavelength than that of the GaAs semiconductor can be produced. However, there is no description of acquiring a long wave the wavelength of which exceeds 1.2 xcexcm. Also, in this invention, there is no suggestion of the problem when plural different optical elements are integrated on a single substrate.
Further, for such a document, Japanese Patent Unexamined Publication No. Hei. 9-328357 can be given. In this document 3, an invention made to form a mixed crystalline semiconductor in Families III to V of large composition of nitrogen to have high quality without enhancing the hole density of Family V is disclosed. To achieve such an object, a method of manufacturing a GaInNAs semiconductor according to a predetermined procedure is disclosed. However, there is no description of structure suitable for integrating optical elements required in a future optical communication network such as a luminous element, an optical waveguide and a diffraction grating. Also, there is no concrete and systematic description of a GaInNAs semiconductor that can be used in an optical integrated circuit including such an optical element and can be applied in a range of wavelengths from 1.25 to 1.65 xcexcm.
Particularly, in these documents, there is no description of applying the GaInNAs semiconductor to a luminous element and adopting the GaInNAs semiconductor for an optical waveguide on which light related to this luminous element is transmitted.
Then, a first object of the present invention is to provide a semiconductor optical device wherein a luminous element, an optical waveguide and an optical element are integrated on a GaAs semiconductor substrate.
A second object of the present invention is to provide a method of manufacturing the semiconductor optical device.
The semiconductor optical device according to the invention is provided with a GaAs semiconductor substrate, an optical waveguide part provided on the GaAs semiconductor substrate and an optical amplification part provided on the GaAs semiconductor substrate. The optical amplification part includes at least one semiconductor optical amplifier. The optical waveguide is optically connected to the semiconductor optical amplifier.
The semiconductor optical amplifier is provided with an active layer including a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor, a first conductive-type clad layer and a second conductive-type clad layer respectively having the active layer between them. The active layer has a refractive index larger than that of the first conductive-type clad layer and that of the second conductive-type clad layer.
The optical waveguide is composed of a core semiconductor layer including at least either of a GaInNAs semiconductor or a GaAs semiconductor, first and second clad semiconductor layers respectively having the core semiconductor layer between them.
The optical element can include an optical multiplexer having plural input ports and at least one output for example. The input ports can be optically connected to the semiconductor optical amplifier. Also, the optical element can include an optical demultiplexer having at least one input port and plural output ports for example. The output ports can be optically connected to the semiconductor optical amplifier. The optical waveguide part can include an optical multiplexer and an optical demultiplexer respectively having an optical waveguide. Each optical multiplexer and each optical demultiplexer can include AWG for example.
In case the core semiconductor layer includes a GaInNAs semiconductor, the GaInNAs semiconductor has a band gap larger than energy for the wavelength of light to be amplified in the optical amplification part. Therefore, absorption in the optical waveguide part is reduced and both light to be amplified in the optical amplification part and light amplified in the optical amplification part can be propagated in the core semiconductor layer. Also, the core semiconductor layer is in contact with the active layer. Therefore, the optical waveguide and the semiconductor optical amplifier can be optically coupled without loss that may be caused by having an air layer between them.
As described above, as the GaAs semiconductor substrate is adopted, optical elements can be integrated on the fine substrate having a large aperture. Therefore, when plural optical elements such as the optical demultiplexer and/or the optical multiplexer and the semiconductor optical amplifier are integrated, an optical element the relative precision of which is equal not only for the composition of the material but for the worked form of the optical waveguide is acquired. Also, as the active layer is made of a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor and each of the optical multiplexer and the optical demultiplexer is provided with the optical waveguide including at least either of a GaInNAs semiconductor or a GaAs semiconductor, light of a wavelength in a wide range can be treated by combining materials of suitable composition.
The optical demultiplexer can demultiplex received light every light to be input to the semiconductor optical amplifier. The semiconductor optical amplifier can amplify the received light or can be operated as a gate. The optical multiplexer can multiplex light processed in the semiconductor optical amplifier.
In the semiconductor optical device according to the invention, the optical demultiplexer can include an arrayed waveguide grating (AWG) and the optical multiplexer can also include AWG. In case the optical demultiplexer includes AWG, light received via the input port of AWG can be demultiplexed into plural output ports provided in spatially different positions every wavelength. Also, in case the optical multiplexer includes AWG, light different in a wavelength received via the plural input ports in spatially different positions can be multiplexed into a single output port.
In the semiconductor optical device according to the invention, for the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor of the active layer, it is possible that 0.7xe2x89xa6xxe2x89xa60.9 and 0.03xe2x89xa6yxe2x89xa60.1.
The semiconductor of such composition is suitable for a bulk active layer having no quantum well (QW) structure. Hereby, these inventors found that light of energy for a band gap of the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor layer adopted as the material of the active layer was generated by controlling the composition in the range.
In the semiconductor optical device according to the invention, the active layer can be provided at least one quantum well layer including a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor and plural quantum barrier layers provided with the quantum well layer between them.
In the semiconductor optical device according to the invention, the quantum barrier layer includes a GaAs semiconductor and for the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor of the quantum well layer, it is possible that x is substantially 0.65, preferably 0.62xe2x89xa6xxe2x89xa60.68 and 0.005xe2x89xa6yxe2x89xa60.04.
The semiconductor of such composition is suitable for an active layer having single quantum well (SQW) structure or multiple quantum well (MQW) structure. These inventors found that in such a range of composition, the mismatching of approximately 2% with a grating was applied between a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor in the quantum well layer and a GaAs semiconductor, and light of energy corresponding to difference in a level between quantums in a conduction band or in a valence band according to the band cap or quantum well structure was amplified by controlling the composition of the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor layer adopted as the material of the quantum well layer in the range described above.
In the semiconductor optical device according to the invention, the quantum barrier layer includes an AlGaAs semiconductor and for the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor of the quantum well layer, it is possible that 0.7xe2x89xa6xxe2x89xa60.87 and 0.035xe2x89xa6yxe2x89xa60.1.
The semiconductor of such composition is suitable for an active layer having SQW structure or MQW structure. These inventors found that in such a range of composition, matching with a grating was substantially achieved for an AlGaAs semiconductor in the quantum barrier layer, and light of energy according to the band cap and the quantum well structure of the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor layer adopted as the material of the quantum well layer was amplified.
In the semiconductor optical device according to the invention, the quantum barrier layer can include at least either of a GaInAs semiconductor or a GaAs semiconductor. For the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor of the quantum well layer, it is possible that 0.7xe2x89xa6xxe2x89xa60.9 and 0.035xe2x89xa6yxe2x89xa60.06.
The semiconductor of such composition is suitable for an active layer having SQW structure or MQW structure. These inventors found that in such a range of composition, so-called type II of quantum well structure was achieved. These inventors found that light of energy according to difference in energy between the conductive layer of the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor layer adopted as the material of the quantum well layer and the valence band of the quantum barrier layer, and according to quantum well structure was generated.
To manufacture the semiconductor optical device described so far and a semiconductor optical device to be described after this, the following methods can be applied.
A method of manufacturing the semiconductor optical device according to the invention is composed of (1) a step for preparing a GaAs semiconductor substrate provided with a first area and a second area on its principal plane, (2) a step for forming an optical amplification part provided with a first conductive type clad layer, an active layer including a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor and a second conductive type clad layer in the first area on the GaAs semiconductor substrate and (3) a step for forming an optical element including an optical waveguide provided with a first clad semiconductor layer, a core semiconductor layer including at least either of a GaInNAs semiconductor having a band gap larger than the GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor or a GaAs semiconductor and a second clad semiconductor layer in the second area on the GaAs semiconductor substrate.
As optical elements such as the optical amplification part, the optical multiplexer and the optical demultiplexer are formed in separate areas, the composition of the active layer film in the optical amplification part and the composition of the core semiconductor film of the optical waveguide included in the optical element can be independently controlled.
Also, as the semiconductor optical amplifier and the optical waveguide are formed on the same substrate, relative precision in the arrangement of the semiconductor optical amplifier and the optical waveguide is high. As the materials and a process of the formation are same in case the optical element includes the optical multiplexer and the optical demultiplexer, the relative precision of the shape is also high.
Further, in case a GaInNAs semiconductor is adopted, light of various wavelengths can be managed only by varying the composition. Therefore, a semiconductor optical device that can manage light of various wavelengths, keeping predetermined relation with the lattice constant of a GaAs semiconductor is provided.
In the method of manufacturing the semiconductor optical device according to the invention, the step (2) described above may be also composed of (2a) a substep for sequentially forming a first conductive type clad film, an active layer film including a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor and a second conductive type clad film on the GaAs semiconductor substrate and (2b) a substep for etching the first conductive type clad film, the active layer film and the second conductive type clad film and forming a first conductive type clad layer, an active layer and a second conductive type clad layer in the first area.
In the method of manufacturing the semiconductor optical device according to the invention, the step (3) described above may be also composed of (3a) a substep for sequentially forming a first clad semiconductor film, a core semiconductor film including at least either of a GaInNAs semiconductor having a band gap larger than a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor or a GaAs semiconductor and a second clad semiconductor film in the second area on the GaAs semiconductor substrate and (3b) a substep for etching the first clad semiconductor film, the core semiconductor film and the second clad semiconductor film to form an optical waveguide including a first clad semiconductor layer, a core semiconductor layer and a second clad semiconductor layer and forming an optical multiplexer and an optical demultiplexer respectively including the optical waveguide.
Also, in the method of manufacturing the semiconductor optical device according to the invention, the step (3) described above may also include (3c) a substep for sequentially forming a first clad semiconductor layer film, a core semiconductor layer film including at least either of a GaInNAs semiconductor having a band gap larger than a GaxIn1xe2x88x92xNyAs1xe2x88x92y semiconductor or a GaAs semiconductor and a second clad semiconductor layer film in the second area on the GaAs semiconductor substrate and (3d) a substep for etching the first clad semiconductor layer film and the core semiconductor layer film to form an optical waveguide including a first clad semiconductor layer, a core semiconductor layer and a second semiconductor layer, at least etching the first conductive type clad layer and forming an optical multiplexer and an optical demultiplexer.
Further, in the invention related to the method of manufacturing the semiconductor optical device, the core semiconductor layer is formed so that it is in contact with the active layer. Also, the first and second clad semiconductor layer films are formed so that they have the core semiconductor layer film between them.
According to the method composed of the steps described above, as the active layer and the core semiconductor layer can be connected in the manufacturing process of the semiconductor optical device in managed environment, loss in coupling can be optically reduced.